Sega Megadrive/Genesis Cartridge Pinout

Sega Megadrive/Genesis Cartridge Pinout
Photo by Adam Mills / Unsplash

I’ve recently been getting into collecting for the Sega Megadrive/Genesis, it’s the one console I had most contact with as a kid. As part of that I’ve been looking at building a tool for verifying cartridges (and maybe making them available like the Retrocade).

As part of that I’ve needed to understand the cartridge, and this is a living summary of my investigations.


The cartridge interface is a 32x2 card edge connector, with a 2.54mm pitch. It’s sides are designated as A and B, of which B is closer to the front of the Megadrive when plugged in.

Additionally, when looking at the front of the megadrive and the cartridge, pin 32 is to the left and pin 1 to the right.

Pin Out

This data has been gather from many different websites, which will be referenced below. All directions are from the Consoles perspective, output is to the cartridge, input is from the cartridge. Output / input pins are tristate, and direction will change for write operations.

Side A

Pin Direction Designation Description
A1 Output GND
A2 Output +5V
A3 Output Address Bit 8
A4 Output Address Bit 11
A5 Output Address Bit 7
A6 Output Address Bit 12
A7 Output Address Bit 6
A8 Output Address Bit 13
A9 Output Address Bit 5
A10 Output Address Bit 14
A11 Output Address Bit 4
A12 Output Address Bit 15
A13 Output Address Bit 3
A14 Output Address Bit 16
A15 Output Address Bit 2
A16 Output Address Bit 17
A17 Output Address Bit 1 This is the first address bit, bit 0 is hardwired to low.
A18 Output GND
A19 Output / Input Data Bit 7
A20 Output / Input Data Bit 0
A21 Output / Input Data Bit 8
A22 Output / Input Data Bit 6
A23 Output / Input Data Bit 1
A24 Output / Input Data Bit 9
A25 Output / Input Data Bit 5
A26 Output / Input Data Bit 2
A27 Output / Input Data Bit 10
A28 Output / Input Data Bit 4
A29 Output / Input Data Bit 3
A30 Output / Input Data Bit 11
A31 Output +5V
A32 Output GND

Side B

Pin Direction Designation Description
B1 Input Left Audio Audio sourced from cartridge, left channel, mixed into output.
B2 Output /MRES Master reset, from system start up.
B3 Input Right Audio Audio sourced from cartridge, right channel, mixed into output.
B4 Output Address Bit 9
B5 Output Address Bit 10
B6 Output Address Bit 18
B7 Output Address Bit 19
B8 Output Address Bit 20
B9 Output Address Bit 21
B10 Output Address Bit 22
B11 Output Address Bit 23
B12 Output /YS VDP is currently drawing the backdrop colour.
B13 Output /VSYNC Vertical sync pulse.
B14 Output /HSYNC Horizonal sync pulse.
B15 Output EDCLK External Dot Clock (~13.4 or 10.7 MHz).
B16 Output /CAS0 Read or Write on $000000-$DFFFFF region.
B17 Output /CEO Chip Enable for the cartridge. Normally low when accessing $000000-$3FFFFF region. When expension unit is present then low when accessing $400000-$7FFFFF.
B18 Output /AS Address strobe, address on bus is currently valid and not changing.
B19 Output VCLK 68K Clock
B20 Input /DTACK Data acknowledge to 68K.
B21 Output /CAS2 Read or Write on $E00000-$FFFFFF region, maybe (Upper 2MB).
B22 Output / Input Data Bit 15
B23 Output / Input Data Bit 14
B24 Output / Input Data Bit 13
B25 Output / Input Data Bit 12
B26 Output /ASEL Read or Write on $000000-$7FFFFF region
B27 Output /VRES System reset, from front panel switch.
B28 Output /LWR Lower byte WRite, the lower byte on the data lines should be written to the location in the address lines.
B29 Output /UWR Upper byte WRite, the upper byte on the data lines should be written to the location in the address lines.
B30 Input /M3 Pulled high in console, cartridge shorts to ground to indicate console should run in Mark 3 (Master System) mode.
B31 Output /TIME Set for r/w at/to $A13000-$A130FF, given the name suggests it might be for a real time clock in the cartridge. This would enable usage as a chip enable on a RTC, using fewer address lines or logic to that RTC. Used in Sonic 3 for SRAM.
B32 Input /CART Pulled high in console, cartridge shorts to ground to indicate presence.